Aminoglycoside antibiotics, for example, streptomycin, kanamycins, gentamicins, tobramycin, etc. have been used practically as broad spectrum antimicrobials effective against gram-positive, gram-negative and acid-fast bacteria. The aminoglycoside antibiotics, however, are sometimes accompanied by undesired side effect such as nephropathy and deafness. Occurrence of resistant strains against the aminoglycosides is another problem to be solved. Recently, it has been attempted to improve the antimicrobial activity and to relatively decrease the side effects by modification of such antibiotics. For instance, amikacin which is prepared by acylation of the 1-amino group of kanamycin A with (S)-4-amino-2-hydroxybutyric acid [Kawaguchi et al, J. Antibiotic 25, 695(1972); U.S. Pat. No. 3,781,268 (1973); J. Antibiotic 27, 677(1974)] is an excellent antimicrobial agent of which the activity is more potent than kanamycin A and of which the toxicity is approximately the same as kanamycin A.